How I replaced Skype with Twilio (2019–2022)

How I replaced Skype with Twilio to make phone calls from my computer.

Motivation

Working remotely, I have become used to the comfort of making calls from my computer on Slack or Discord. Using a quality headset gives a warm sound and a feeling of proximity, and leaves the hands clear for typing on the keyboard and looking up information during the call.

I have been a longtime subscriber of Skype premium service to get a similar experience when calling regular phones instead of other computers. Sadly, as the Skype service stagnated for many years before changing for the worse in 2017–2018, I had to find a better alternative and I started to look into VOIP services with support for calls to the PSTN in 2018–2019.

The Long Story

This is the story of how I successfully configured Twilio to get a mobile phone number which can make and receive calls from my computer.

I have described all the steps that I followed in details, including the understanding that I gained through trial and error, in separate issues:

If you are interested only in how to reproduce my current setup, you can read the short story below. It features links to more details in the long story, if you need them.

The Short Story

1. Create your Twilio account

if you do not have a Twilio account, sign up
or if you already have a Twilio account, sign in

2. Choose a new phone number

3. Configure SIP

create a SIP user for yourself
create a SIP domain for your Twilio phone number
download and install Linphone on your computer
configure call encryption and add the SIP user in Linphone

4. Make calls from your computer

create a TwiML script which describes how phone calls made from the computer are forwarded to regular phones:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Making Calls from SIP to Regular Phones -->
<Response>
  <Dial callerId="{{#e164}}{{SipDomain}}{{/e164}}">
    {{#e164}}{{To}}{{/e164}}
  </Dial>
</Response>

copy the URL of the TwiML bin, found in its details after saving the script.
go to the settings of the SIP domain, and under Voice Configuration, paste the URL from the clipboard into the Request URL field
save the settings of the SIP domain
launch Linphone on your computer
test the setup: call a regular phone number from Linphone
you can then save this phone number as a contact

5. Receive calls on your computer

create a new TwiML script which describes how phone calls received from regular phones are answered:

<?xml version="1.0" encoding="UTF-8"?>
<Response>
  <!-- Receiving Calls from Regular Phones to SIP -->
  <Dial>
    <Sip>sip:me@1-202-555-0162.sip.us1.twilio.com;transport=tls;secure=true</Sip>
  </Dial>
</Response>

In the above script, replace the user name and domain in the <Sip> element with the identifier of the SIP user that you created, followed with @ and the SIP domain that you created, ending with .sip.us1.twilio.com;transport=tls;secure=true:

<Sip>sip:[SIP User]@[SIP Domain].sip.us1.twilio.com;transport=tls;secure=true</Sip>

go to the configuration of your phone number on Twilio
next to "A call comes in", select TwiML and the script that you just created to manage incoming phone calls
delete the URL next to "A message comes in", which answers all texts with a canned response
save the settings
try to call your Twilio number from a regular phone

6. Configure a voicemail

You can extend the TwiML script which handles incoming calls to forward the caller to voicemail when you fail to answer:

record a voicemail greeting using Audacity
export the greeting as a WAV file (in mono with 8bit/s at 8kHz)
upload the WAV as an asset on Twilio
copy the URL of the asset
go to the Voicemail Twimlet
[create a custom Voicemail URL][] using the generator form at the bottom of the page:
- Email: the email address where you want to receive voicemail notifications
- Message: the URL of your greeting, pasted from the clipboard
- Transcribe: false
copy the generated URL
go to the Forward Twimlet
create a custom Forward Twimlet URL: paste your custom Voicemail URL next to FailUrl in the form at the bottom of the page, then change its protocol from http to https
leave all the other fields empty
copy the generated URL
go back to your Twilio dashboard
in the TwiML bin which handles incoming calls, add an action attribute to the <Dial> element
paste your custom Forward URL as its value
change the protocol of the URL from http to https
then add &Dial=true at the end of the URL

You now have a script of the form:

<?xml version="1.0" encoding="UTF-8"?>
<Response>
  <!-- Receiving Calls from Regular Phones to SIP (with Voicemail) -->
  <Dial action="https://twimlets.com/forward?FailUrl=https%3A%2F%2Ftwimlets.com%2Fvoicemail%3FEmail%3Dyou%2540example.org%26Message%3Dhttps%253A%252F%252Fyour-runtime-domain.twil.io%252Fassets%252Fgreeting.wav%26Transcribe%3Dfalse&amp;Dial=true">
    <Sip>sip:your-sip-user@your-sip-domain.sip.us1.twilio.com;transport=tls;secure=true</Sip>
  </Dial>
</Response>

where:

you@example.org stands for your email address
https://your-runtime-domain.twil.io/assets/greeting.wav stands for the URL of your greeting asset
your-sip-user stands for the SIP user that you created for yourself
your-sip-domain stands for the custom SIP subdomain that you created
you can now close your computer and call your Twilio number from a regular phone to test the voicemail

7. Configure Pipedream Workflow to Send SMS Messages by Email

create your Pipedream account]
a new workflow is created automatically, rename it to Send SMS by Email
select the Email action for the trigger step of the workflow
send a test email to the inbound email address of the workflow

When sending an SMS by email, you will need to include the phone number of the recipient, in international format, in the subject, e.g. New SMS to +## ###-###-#####.

the test event is received by your Pipedream workflow
continue and add the Twilio: Send SMS action as a second step
create a Twilio API key and connect Pipedream to Twilio API
select your Twilio phone number as From
configure the following template as To:

{{steps.trigger.event.headers.subject.replace(/^.+\+/,'+').replace(/[^+0-9]/g,'')}}

configure the following template as Message Body:

{{steps.trigger.event.body.text}}

test and deploy the configured workflow

8. Configure Pipedream Workflow to Receive SMS Messages by Email

create a new workflow
name it Receive SMS by Email
select HTTP / Webhook Requests as trigger step of the workflow
configure a static response for the webhook, with status code 200, header Content-Type:application/xml and the static response below:

<?xml version="1.0" encoding="UTF-8" ?>
<Response/>

configure the trigger URL as webhook for incoming SMS in Twilio dashboard
send a test SMS to your Twilio phone number
the test event is received by your Pipedream workflow
continue and add the Send Email action as second step of the workflow
configure the template below as Subject:

New SMS from {{steps.trigger.event.body.From}}

configure the template below as Text:

{{steps.trigger.event.body.Body}}

test and deploy your second workflow

Limitations

The current setup does not fulfill all of my expectations yet:

even for calls from Europe to Europe, the call always transits through a Twilio server in the US, increasing latency

License

Code: CC0 (no attribution required)
Text and Images: CC-BY Eric Bréchemier

eric-brechemier / how-i-replaced-skype-with-twilio

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